Microstructure and electromagnetic properties of flake-like Nd–Fe–B nanocomposite powders with different milling times

The microstructure and electromagnetic properties of melt-spun Nd–Fe–B nanocomposites, which have been dealt with by the ball milling process with different milling times, are studied specifically in this paper. The powder size ranges from 20 μm to 5 μm after different milling times. Moreover the powder particles even remain flake-like shape after 11 h milling time. X-ray diffraction spectra strongly suggest that all samples only have the single α-Fe phase. By using the complex permeability (μ = μ′ − μ″) and permittivity (ε = ε′ − ε″) within 2 to 18 GHz frequency range, determined by vector network analysis, the experiment shows that the permeability of flake-like Nd3Fe68Co18B11 can be increased while its permittivity is decreased by increasing the milling time. For the sample with 11 h milling time, its imaginary permeability μ″ can be increased to an abnormal state below the frequency of 6 GHz. Based on transmission line theory, it is calculated that the Nd3Fe68Co18B11 composites can achieve their optimal reflection loss (RL = − 8 dB) at 3.7 GHz with a matching thickness of 1.5 mm. This paper shows the possibility to obtain good microwave absorbing properties at a proper milling time for melt spun Nd–Fe–B nanocomposites.